tripping main switch

[timtheenchanter]

I seem to have a strange problem/nuisance.

A couple of times i have had to replace a socket/ light fitting.
as per sense and safety i turn of the breaker for the particular ring i am working on, checking with a voltage detector all is dead before starting.

My problem is this, whilst working on the live/neutral all is fine, but when ever i touch the earth the main breaker trips, leaving the house with no power.

Is there a problem with the consumer unit and/or main breaker, or am i just charged with too much static????

 

[Adam_151]

What is the main breaker, an RCD or an ELCB?,

are you touching earth to neutral? a breaker doesn't disconnect neutral, and a neutral to earth short will trip an RCD (if it is passing load)

 

[timtheenchanter]

its a Wylex RCD 80A Rated 100mA trip

 

[timtheenchanter]

sorry, meant to answer the second bit, as far as i can tell, its when i touch the earth with my fingers, i unless i happen to catch the earth with the neutral, would there be a load on the neautral with everything off, braker off?

 

[andy]

sorry, meant to answer the second bit, as far as i can tell, its when i touch the earth with my fingers, i unless i happen to catch the earth with the neutral, would there be a load on the neautral with everything off, braker off?

if you neutral and earth touch, electricity will pass between and trip the RCD. you have to disconnect neutral from inside the CU to avoid it

 

[Adam_151]

Sorry, I phrased that badly, if the RCD is passing load, not the neutral passing load.

For example if someone was using an electric shower, the current for that will be flowing through the RCD, you might have the breaker for the sockets off and be replacing a broken faceplate, if you touch neutral to earth, because of the slight difference in potential between neutral and earth, you will have created another path for some of the current from the shower to get to earth/neutral through, its only going to be a very small current, and the majority of the current will be flowing the usual way, but it will be enough to unbalence the RCD* and cause it to trip

RCDs work on detecting leakage to earth by comparing the live and neutral currents, if they arn't the same, then current must be flowing somewhere it should, and if the difference exceeds the rating of the RCD, it trips

The cure for it is to isolate neutral when working on a circuit, chances are the only way to do this is to disconnect it from the neutral block in the CU, or just try your best to not let them touch (but theres always the time you forget, and cut through a cable that has only been isolated on phase, and the RCD trips out, and you get the wrath of someone who has lost work on a computer...)

 

[timtheenchanter]

Ah-Ha, that may be the cause, although so far, ist onle been the wrath of the OH losing the veiwing pleasure on an Eastenders omnibus!!!